1. Field of the Invention
This invention relates to high-velocity liquid jet cutting and, in particular, an improved nozzle and mounting assembly.
2. Prior Art
The use of fluid jets for cutting has been the subject of continuous experimentation and refinement. Fluid jets for cutting, drilling and the like are well known and utilized for hydraulic mining and other rough cut operations. Patents such as Chaney, U.S. Pat. No. 3,554,602, and Goodwin, et al., U.S. Pat. No. 3,419,220, are typical of a host of prior art which recognizes the use of fluid cutting as a basic technique. More recently, with the advent of computer technology, fluid jet cutting has reached a refined state where, by the use of collimated jet streams, cutting with a narrower kerf is possible providing a better finish along cut surfaces. Accordingly, fluid jet cutting has found application in such commercial areas as high-quality mass production cutting of shoe inner liners and soles, dress patterns and the like. A typical system is found in U.S. Pat. No. 3,978,748 wherein a composite fluid jet computerized cutting system is shown. In such systems, the movement of the jet is controlled by computer such that cutting paths across the cutting table are maximized for production output.
One area of continuing research in fluid jet cutting is the problem of dispersion of the jet, both as it leaves the nozzle and also as it passes through materials to be cut. Accordingly, the prior art is replete with a number of concepts for avoiding dispersion to thereby reduce the wetting of the material being cut and provide a better finish along the surfaces so cut by the high-pressure nozzle.
One prior art attempt is shown in Franz, U.S. Pat. No. 3,750,961. In that patent, a high-velocity fluid jet nozzle is shown utilizing a heavy walled vitreous body having a jet orifice of substantially greater length than the cross-section diameter of the orifice itself. The orifice is defined by a smooth surface which blends into an entry chamber defined by the vitreous body. This system attempts to reduce the problem of dispersion by careful contouring and the reduction of upstream hydrodynamic turbulence.
Another approach is shown in Chadwick, et al., U.S. Pat. No. 3,756,106, where a corundum crystal having an orifice of specific geometry is capable of producing a well-defined fluid cutting jet. While all of these prior art nozzles are directed toward the achievement of a better shaped jet by providing carefully contoured surfaces of particular geometric relationships, one problem which remains is that of leakage around the nozzle elements themselves.
A recent attempt at providing a collimated jet stream which reduces kerf widths, thereby improving the finish of the cut surfaces, is shown in Thomas, et al., U.S. Pat. No. 3,997,111. In Thomas, et al., collimation of the jet occurs by having a housing interconnected between the source of fluid under pressure and the nozzle. The housing defines a flow collimating chamber located directly upstream of the nozzle to receive the liquid from the high-pressure generating equipment and deliver the liquid directly to the chamber for expulsion. This flow chamber which provides the collimation function is of a specific ratio to the discharge opening of the nozzle. Thomas, et al. specifies the minimum ratio of the cross-sectional area of the flow chamber to be one hundred times that of the discharge opening of the nozzle, and preferably greater than two hundred times that of the nozzle. An outside range is approximately 1400 times as set forth in the specification of that patent. While collimation occurs producing very narrow diameter jets, in actual practice, the system defined in U.S. Pat. No. 3,997,111 has been susceptible to various mechanical breakdown phenomena. In order to improve the problems of nozzle handling and leakage about the nozzle, Thomas, et al. utilizes a washer or mounting ring about the sapphire nozzle such that a deformation takes place when the system is under pressure. The sapphire nozzle in Thomas, et al, is mounted in an elastically deformable washer or mounting ring. This ring is to provide a seal between the nozzle element and the nozzle housing and to exert uniform pressure radially to the sides of the nozzle element. This elastic ring, accordingly, is designed to prevent cracking of the sapphire nozzle element or damage to it, and to reduce the tolerance requirements between the lateral surface of the counterbore and the lateral surface of the nozzle element, and to provide an adequate seal between the nozzle element and the bottom wall of the nozzle housing against which the nozzle element rests.